The invention relates generally to a gate or stopping device for automatically stopping a flow of objects such as containers moving along a conveyor in a processing line.
Conveyor systems such as guideways or chutes are conventionally used in the food and beverage industry to process cans and other similar containers. The conveyor carries the containers in a generally continuous flow to various pieces of machinery such as automatic fillers. At certain points in such a conveyor system it is necessary or desirable to temporarily stop the flow of containers, for example to service machinery, remove a blockage, or control the flow rate. Gates, often called can stops, are installed along the conveyor at selected points for this purpose.
One type of prior art can stop is shown in FIG. 7 of U.S. Pat. No. 3,185,277 and consists of an arm (37) which can be pivoted into the path of containers moving on a conveyor. The pivoting arm is normally held out of the path of the containers by means of a conventional tension spring (39). A pneumatic actuator is used to overcome the tension of the spring and move the arm into the path of the containers. The use of such a tension spring for biasing the gate arm presents several disadvantages. First, a tenion spring tends to be non-linear, requiring increased force to stretch the spring as it becomes elongated. The maximum force exerted by the gate closing actuator must therefore be enough to overcome the maximum spring force exerted, which is developed when the gate is closed and the spring is the most elongated. The amount of actuator force is excessive, however, when the gate is just beginning to close and the biasing spring is shorter and exerts less force. The non-linearity of the spring consequently produces a swift and excessively energetic movement of the gate arm when it begins to move, tending to dent or damage light containers such as empty aluminum cans. A second disadvantage of using a tension spring for biasing the gate arm of a conveyor gate is its exposed location. Because the spring pulls the gate arm out of the path of the containers, it is generally located outside of any protective housing and often gets caught and broken by employees monitoring or servicing the conveyor line. Another inherent disadvantage of tension springs is that they have a relatively short life and will fatique and break in time. If a tension spring should break while the conveyor line is operating, it could present the problem of pieces being scattered and falling into nearby containers.
Prior art can stops which utilize pneumatic actuators are provided with pneumatic diaphragms formed of 1/16 inch neoprene which tends to rupture if exposed to the full line pressure of the pneumatic systems most commonly used in canning facilities. Rupture is normally prevented by operating the actuator through a flow control valve which reduces line pressure. Such flow control valves reduce standard line pressure from approximately 120 pounds per square inch (p.s.i.) down to 10-25 p.s.i. Whenever a flow control valve fails, the full line pressure of 120 p.s.i. enters the pneumatic actuator and rapidly ruptures the diaphragm, necessitating repair and causing delay.